CD20 is a transmembrane protein that is expressed on more than 95% of B-lymphocytes. Expression at the cell surface occurs from the pre-B stage of development until differentiation to a plasma cell. The protein has several functions; it serves as a calcium channel, it is involved in intracellular signal transduction, and it can modulate cell growth and differentiation. In human medicine, anti-CD20 monoclonal antibody therapeutics (e.g.: RITUXAN® (Rituximab) by Genentech and IDEC Pharmaceuticals) have been successfully utilized to treat relapsed or refractory low-grade or follicular, CD20+, B-cell non-Hodgkin's lymphoma (NHL). RITUXAN® (Rituximab) has also been used in treating immune-mediated hemolytic anemia, immune-mediated thrombocytopenia, and systemic lupus erythematosus (SLE). RITUXAN® (Rituximab), however, does not bind canine B cells. See, Impellizeri et al., Vet. Cancer Society. 2003. Proceed. 23rd Ann. Conf., p. 2.